Prior Art
Approximately 5,000-6,000 tons/year of calcium sulfate hemihydrate plaster are used for medical support. About 75% of the 4 million casts applied each year in the U.S. are for setting fractures; others are for support of sprained limbs and orthopedic immobilization. These conventional plaster of Paris systems however have many unsatisfactory properties; the casts formed therewith are heavy, X-ray impervious, absorb excessive moisture which has a detrimental effect on the physical properties, are difficult to clean, lack elasticity, are slow to reach ultimate strength, have poor abrasive resistance, and are receptive to bacterial and fungal growth.
There is probably nothing that can be done to overcome all of the problems of wearing a cast, splint, or brace. But through extensive research and development programs the chemical industry is helping to lighten the load and remove some of the inconveniences.
Along the lines of lightening the weight of rigid enclosures and elimination other disadvantages methods have been proposed which utilize polymerizing systems.
The prior art consists essentially of bandages imbued with heat or light curable polymers. As an example of such art U.S. Pat. Nos. 2,576,027, 3,027,336, 3,089,486, 3,421,501, and 3,613,675 may be cited.
Furthermore, more specifically and more closely related to our invention we may also cite U.S. Pat. Nos. 3,375,822, 3,745,998, and 2,969,791.
U.S. Pat. No. 3,375,822 discloses a surgical cast comprising a sealed envelope containing a plurality of low density spheres and a binder material.
U.S. Pat. No. 3,745,998 teaches a cast comprised of a nonporous elastic envelope with an air evacuation tube.
U.S. Pat. No. 2,969,791 teaches an article comprising a woven, open-mesh fabric of textile material. The fabric is dipped in an emulsion of a plastic material including a bonding agent and dried. Just prior to use the thus treated fabric is dipped in or sprayed with a solvent and applied on the body member. The solvent is allowed to evaporate thus causing the applied fabric to rigidify.
In most of these systems however large amounts of liquid volatiles are employed and the increased temperatures required for cure render their use in confined areas undesirable and furthermore high molding temperatures require that an insulating medium be introduced between the curable polymer and the skin which compromises the ability to shape or mold said polymeric layer to the immobilized part satisfactorily.